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Forum: Pentax K-1 1 Day Ago  
JPEG too soft for Pixel Shift
Posted By photoptimist
Replies: 5
Views: 304
Interesting!

I had always assumed that setting the JPEG quality to the highest setting would essentially be a lossless setting. In theory, it's true but it seems many apps don't support it. JPEG - Wikipedia says " The JPEG standard includes a lossless coding mode, but that mode is not supported in most products."

A Pixel Shift image at base ISO probably has so little noise in it that even the mildest amount of compression can only happen at the expense of image detail.
Forum: Ricoh GR 1 Day Ago  
Indoor Candids
Posted By photoptimist
Replies: 3
Views: 226
The high ISO performance of the sensor in the GR III is going spank the pants off the Pixel 3 phone. You'll get much cleaner images and be able to freeze motion in lower lighting conditions.
Forum: Pentax DSLR Discussion 2 Days Ago  
A supposition with a question.
Posted By photoptimist
Replies: 29
Views: 773
Consider this pair:
A K-5 w 50mm set to f/2.8, 1/200sec, ISO100
A K-1 w 75mm set to f/4, 1/200sec, ISO200

They'll have identical exposure, motion blur, DoF, and overall DR. However, the K-1 image will probably have better sharpness both because it has more than 2X the pixels and because the lens is being used closer to it's sweet spot of maximum resolution.

Overall, you'll find that the K-1's higher DR, better color accuracy and higher resolution really do offer some advantage beside shallow DoF. Whether that better DR and resolution is "worth it" to you depends on you.
Forum: General Photography 2 Days Ago  
What is 'correct' exposure ?
Posted By photoptimist
Replies: 16
Views: 487
There are at least three definitions of the "correct" exposure:

1) Exposure to exactly match the reflectances or brightnesses of the scene with the final image. This exposure ensures that anything that is 18% gray in scene is also 18% gray in the final photograph.

2) Exposure to capture all the highlights and shadow details that the human eye can see. This exposure ensures no highlights are clipped and no shadows are muddy but it may require HDR because the dynamic range of the scene might exceed the dynamic range of the camera or output media.

3) Exposure for creating a specific mood which often calls for intentionally over- or under-exposure settings compared to definitions 1 and 2. For example, over-exposing a summer beach scene might intensify the feeling of light and warmth. Or under-exposing a portrait might convey a sense of night-time intimacy or amplify the sadness of the subject. The high-key and low-key genres often intentionally expose in ways that destroy extraneous details which helps focus on the subject.
Forum: Pentax SLR Lens Discussion 2 Days Ago  
A simple question with possibly no answer.
Posted By photoptimist
Replies: 29
Views: 791
As others have said, the 50-200 adds little to your kit.

Instead, a dedicated macro lens would give a big boost to your flora photos. Super zoom macro lenses rarely provide high quality or high magnification. Something like the DFA 100/2.8 dramatically expands the range of close-up shot you can take.
Forum: Digital Processing, Software, and Printing 2 Days Ago  
How Linear Are Some Pentax Camera Sensors?
Posted By photoptimist
Replies: 15
Views: 584
LOL!

Pentax probably used 1.3 instead of 1.25992104989 for the cube root of 2. That approximation would create about a 3.2% error if each full-stop value was divided by 1.3 and multiplied by 1.3 to get the next shorter and next longer 1/3 stop value respectively.
Forum: Digital Processing, Software, and Printing 3 Days Ago  
How Linear Are Some Pentax Camera Sensors?
Posted By photoptimist
Replies: 15
Views: 584
Wow! Great work! And reassuring results!

There are a few of potential sources of the tiny amount of non-linearity in the data:

1) Unless you used the electronic shutter, some of the nonlinearity might be in the nonuniformity or inaccuracy of the mechanical shutter.

2) And even if you use the electronic shutter, then some of the some of the nonlinearity might be due to imperfections in the electronic first curtain which probably don't perfectly empty the well during a reset. These will bias the shutter time results in a way that makes the slope a bit shallower.

3) Dark current (including dark current between when the shutter closes and the read out gets the pixels) would slightly lift the pixel values. You might find the slope of the line differs between the upper edge and the lower edge of the sensor based on the lower or greater delay between curtain and read-out.
Forum: Pentax Film SLR Discussion 3 Days Ago  
Nuclear Blast Camera
Posted By photoptimist
Replies: 14
Views: 495
That's probably what it did unless they either replaced the photosensitive paper every day or used somethng with severe reciprocity failure so it would not eventuallly fog with exposure to day light.

It may be a variant on the https://en.wikipedia.org/wiki/Campbell–Stokes_recorder that records sun intensity by letting a spherical lens burn a track into a sheet of special paper. The paper is treated so that it can't ignite but will char to show when the sun was shining.
Forum: Pentax News and Rumors 3 Days Ago  
New K-series DSLR under development to be exhibited
Posted By photoptimist
Replies: 2,707
Views: 166,942
The interval composite setting with 2 shots can capture the ghostly image of Schrödinger's half-there/half-gone cat.
Forum: Pentax News and Rumors 3 Days Ago  
New K-series DSLR under development to be exhibited
Posted By photoptimist
Replies: 2,707
Views: 166,942
As cool as eye-controlled focus sounds, it's not very compatible with how human vision works.

People's eyes are constantly in motion, twitching over different parts of the scene about 3 times per second. It's kind of like panoramic tiling with a telephoto lens and it's how human vision builds up a detailed view of the world. That's especially true of photographers who might be (should be!) checking all the other non-subject elements in the foreground, background, and borders of the photo.

Although the camera can follow the photographer's eye, it can't read the photographer's mind to know when the eye is looking at the subject or is looking elsewhere in the scene. Thus, a eye-controlled AF system would tend to jump all over the scene as the photographer makes these unconscious eye movements.
Forum: Pentax DSLR Discussion 3 Days Ago  
Automatic Hyperfocal
Posted By photoptimist
Replies: 26
Views: 621
Exactly!

With a good infinity hard stop, a lens could run out to infinity and then back-off the appropriate number of ticks. The camera would still need some kind of user-entered CoC value.

The more general problem of knowing or controlling the distance setting of the lens requires some sort of highly accurate encoder inside the focus motion system. A 50/1,4 would probably need an 8 or 9 bit encoder (some 8 or 9 tracks with up to 256 or 512 on/off transitions) for sufficient accuracy for professional use on high-resolution cameras.
Forum: Pentax DSLR Discussion 3 Days Ago  
Automatic Hyperfocal
Posted By photoptimist
Replies: 26
Views: 621
Good point! And then there's the change in CoC for pixel peeping instead of printing 8x10.
Forum: Pentax DSLR Discussion 4 Days Ago  
Automatic Hyperfocal
Posted By photoptimist
Replies: 26
Views: 621
As you correctly note, calculating the hyperfocal distance is easy.

Unfortunately, setting the lens to exactly that hyperfocal distance is hard. Most modern lenses don't have an accurate electronic distance scale or reliable infinity setting.
Forum: General Photography 4 Days Ago  
Manual White Balance Not Giving Temp
Posted By photoptimist
Replies: 21
Views: 371
Not everything is an approximation. It's "color temperature" that is a very poor approximation of white balance for most of the light sources found in the modern world. I agree with Steve's hypothesis is that Sony's reported "Color Temperature" number would not be useful for the purpose of picking gels to match it.

That said, I agree with you that it would be nice if Pentax' MWB implementation provided some indication of where a given measured MWB is on the blue-amber and magenta-cyan axes. If it did that, you could do your own measurements of each gel, write them down, and then know which one to use when you measured the scene.
Forum: Pentax SLR Lens Discussion 4 Days Ago  
shadow around the picture
Posted By photoptimist
Replies: 19
Views: 449
^^^^^THIS^^^^

It could also be from adding a thick filter (e.g., polarizer) or a stack of filters
Forum: Pentax Q 4 Days Ago  
Dual Q wild thought
Posted By photoptimist
Replies: 15
Views: 426
Great idea!

And a set of six Qs arranged in a cubical configuration would provide higher and more uniform resolution.

Behold the Qube!
Forum: Pentax K-3 4 Days Ago  
Shake Reduction in the K-3
Posted By photoptimist
Replies: 7
Views: 341
My experience with the K-5 and K-1 suggests that SR performance is linear with focal length and is typically a couple of stops. Thus, I'll use a 300 mm lens with shutter speeds as slow as 1/90 or 1/60. Coffee, hunger, and wind degrade SR performance. A calm mind, calm wind, and solid footing can help. For extra assurance, I sometimes squeeze off a couple of shots with deep breathes in between each one to maximize the chance of a sharp "keeper."

Note: SR on a monopod or tripod can be tricky and is generally not recommended. Depending on the exact structural properties of the support, head, and the mass of the lens, the use of SR on a pod might work well or might be an absolute disaster. Under some conditions, the control loop for the SR system can make the camera-tripod system vibrate violently. If you put the camera on a tripod, enable liveview, zoom in on the screen, you can sometimes see the effect. Instead of stabilizing the live view image, the SR system will make in vibrate. In the worst situations, the thing sounds like a very angry wasp.
Forum: General Talk 4 Days Ago  
Your latest acquisition
Posted By photoptimist
Replies: 17,411
Views: 1,185,778
Probably only if the lens is mounted on an FF camera with no IBIS.

The "perfect" hood for a given lens needs to be shaped for the exact dimensions of the working sensor area (including IBIS motion) so that the hood blocks as much stray light as possible without ever vignetting any rays that would pass through to the sensor. Thus Sigma would need to make four variants of the hood: APS-C, APS-C+IBIS, FF, and FF+IBIS.
Forum: General Photography 4 Days Ago  
Manual White Balance Not Giving Temp
Posted By photoptimist
Replies: 21
Views: 371
Color temperature is a one-axis color balancing system that only works with some light sources.

MWB is a two axis color balancing system -- adjusting the color on both a blue-amber axis and a magenta-cyan axis. Thus Pentax doesn't give the temperature of MWB because it would be inaccurate.
Forum: Photo Critique 5 Days Ago  
Abstract Old Cedar Ave Bridge Cable
Posted By photoptimist
Replies: 16
Views: 305
Interesting subject matter! And tricky to decide what to do about it.....

What I like about it:
-- the lush green background is a nice counterpoint to the cold metal
-- it definitely elicits a "what is that" mystery in the mind of the viewer
-- the corner-to-corner diagonal composition works well


You might try:
-- making the point of focus more in the foreground (and still on the twisted cable)
-- narrowing the aperture to get a bit more detail (maybe f/11?)
-- the lower-right nut needs to be either more in the frame (it's like a cut-off foot) or totally cropped to the straight part of the rod.

Overall, I'd try this with the twisted cable in the foreground on the lower-right, the focus on the cable-to-fitting junction @ the lower-right 1/3-1/3 grid line, and the steel nut/rod bit trailing off into the upper-left background. You might also try equalizing the amount of in-focus twisted cable in one corner with the amount shiny de-focused straight rod in the opposite background corner.

The subject matter looks worthy of more exploration!
Forum: Pentax K-1 5 Days Ago  
Use of LCD screen
Posted By photoptimist
Replies: 20
Views: 456
The top plate LCD on the K-1 is most useful for tripod work (assuming you don't have a tall, eye-level tripod). You can also use it to show exposure settings on the top LCD instead of cluttering the live view image.

The other hidden genius feature of the top LCD is that, when you turn off the camera, the top LCD briefly shows the number of shots remaining on the currently selected SD card. It can be a good habit to glance at that number every time the camera is turned off to reduce the chance of the dreaded "card-full" error.
Forum: Pentax News and Rumors 5 Days Ago  
New K-series DSLR under development to be exhibited
Posted By photoptimist
Replies: 2,707
Views: 166,942
In this day and age, an internet naming contest would inevitably force the use of:

Camera McCameraface
Forum: Pentax SLR Lens Discussion 6 Days Ago  
Focal length = focal length, I know . . . . . . . . . . BUT
Posted By photoptimist
Replies: 131
Views: 2,274
The downsampling algorithm I mentioned is known as "nearest neighbor interpolation" and is the simplest, fastest way to resample a raster image. It's still used where speed of resampling matters.

But for better IQ, especially with non-integer resampling ratios, there are better algorithms such as those mentioned at Image scaling - Wikipedia
Forum: General Photography 10-07-2019, 05:30 PM  
Should Pentax bring “extended ISO” back to the new APSC or future FF flagship body? –
Posted By photoptimist
Replies: 18
Views: 696
More ISO range is always nice although a fraction of a stop of extension would hardly make that much difference.

The question that I've never seen addressed is the IQ effects of the mode? Why make it a special setting unless it has a downside? I'm wild-ass guessing that that the mode might be prone to some fixed pattern noise in the brightest pixels if not all the pixels have a full well capacity that allows that extended ISO. That is, some pixels might saturate at less than 100% of the value range.

That said, it could be especially useful for extended highlight protection -- the camera might set exposure for ISO 100, run the sensor at ISO 50 and provide more protection for the small parts of the image that would other wise blow out.
Forum: Pentax SLR Lens Discussion 10-07-2019, 02:57 PM  
Focal length = focal length, I know . . . . . . . . . . BUT
Posted By photoptimist
Replies: 131
Views: 2,274
I'm glad I can help.

Maybe one way to look at digital things is in terms of how far the various parts move as they read, process, and output the pixels.

In the K-1, the read-out circuit essentially moves over about 0.005 mm to read each successive pixel.

In the computer, a bit of software might downsample the image 2:1 by moving through the input camera file and skipping every other pixel. Now the downsampled pixels in the output file come from 0.010 mm apart on the sensor.

Finally a 300 PPI printer, would deposit the downsampled pixels on 8" x 12" paper with the printhead moving 0.084 mm (1/300") for each 0.010 mm downsampled pixel in the output file.

The end result of this electro-mechanical scaling is an 8.4X magnification from the original optical image features to the printed image features on paper.
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